1. Field of the Invention
The present invention generally relates to a developer amount detector for detecting an amount of developer in a unit that is removably installable in an image forming apparatus by using optical elements, an image forming apparatus incorporating the developer amount detector, and a positioning structure for positioning the unit within the image forming apparatus.
2. Description of the Background Art
Image forming apparatuses such as copiers, printers, facsimile machines, plotters, and multifunction machines capable of at least two of these functions in which components in the image forming apparatus are formed as modular units and the respective units are removably installable in apparatuses have been widely developed. In particular, a process unit in which a development device, a toner cartridge, and a photoreceptor are formed as a single integrated unit is known. As developer contained in the process unit is consumed in use, however, it is necessary to notify users when it is time to replace the process unit. Accordingly, a variety of detection systems to detect an amount of the developer in the process unit have been proposed.
One type of detection system is a light transmission detector that utilizes optical elements. The light transmission-type detector for detecting the amount of the developer irradiates light into a developer container that contains the developer, and the amount of the developer is detected based on a length of time needed for the light to transverse the container and a timing with which the light is detected.
More specifically, the light-transmission detector is constituted by, for example, a light-emitting element, a light-receiving element, and first and second light-guiding members constituted by prisms and mirrors provided in a process unit. With this configuration, the light emitted from the light-emitting element is guided to the developer container in the process unit through the first light-guiding member, and the light thus guided to the developer container is then guided out of the developer container to the light-receiving element through the second light-guiding member. The amount of the developer is determined by a time period during which the light-receiving element receives the light and a timing at which the light-receiving element receives the light.
However, when the process unit is installed in the image forming apparatus, positions of the first and the second light-guiding members can be displaced relative to positions of the light-emitting element and the light-receiving element provided in the image forming apparatus, which degrades detection accuracy.
In order to solve this problem, JP-H02-284165-A proposes a configuration in which a light-receiving element is attached to the image forming apparatus via a rotary lever. With this configuration, when a process unit is installed in an image forming apparatus, the process unit contacts the rotary lever and rotates it to the light-receiving element is accurately relative to the process unit.
However, in this configuration, the rotary lever and a big link mechanism to rotate the rotary lever are required, which increases both the number of components and the size of the device, which in turn increases costs.